Refrigeration system for gas liquefaction



June 27, 1967 J. w. PQERVIER 3,327,488

REFRIGERATION SYSTEM FOR GAS LIQUEFACTION Filed April 17, 1964 INVENTORJAMES W. PERVIER Sham- 6 W A TTOR NE Y1 United States Patent 3,327,488REFRIGERATION SYSTEM FOR GAS LIQUEFACTION James W. Pervier, London,England, assignor to Air Products and Chemicals, Inc, Philadelphia, Pa.,a corporation of Delaware Filed Apr. 17, 1964, Ser. No. 360,556 5Claims. (Cl. 6213) This invention relates to refrigeration and moreparticularly to a refrigeration process employing a plurality of workexpansion stages.

Quite frequently it is desirable to provide a process for producingvariable levels of refrigeration. For example, in the separation ofgaseous mixture, the process may be operated to produce components ofthe gaseous mixture in gaseous phase and it may be desirable at times toproduce components in liquid phase. The diflerent refrigerationrequirements for such performance have been diflicult to achieve witheflicient-cy by an internal refrigeration cycle which is preferredbecause of simplicity and low capital expense.

It is accordingly an object of the present invention to provide a novelrefrigeration process.

Another object is to provide a refrigeration process of varying capacitywhich operates at relatively high efliciency.

Another object is to provide a refrigeration process having theforegoing characteristics which employs a plurality of expansionengines.

Still another object of the present invention is to provide a novelprocess for low temperature separation of gaseous mixtures which iscapable of producing different components in different phases atdifferent times.

Still another object is to provide a low pressure cycle for lowtemperature separation of gaseous mixtures designed to producecomponents of a gaseous mixture in gaseous phase and provided with anovel refrigeration process which makes it possible to produce at leasta portion of at least one component in liquid phase without increasingthe pressure of the gaseous mixture fed to the cycle and withoutrequiring extraneous refrigeration producing means.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in connection withthe accompanying drawing which discloses one embodiment of theinvention. It is to be expressly understood however that the drawing isdesigned for purposes of illustration only and not as a reference forthe definition of the limits of the invention, reference for the latterpurpose being had to the appended claims.

The single figure of the drawing discloses a novel refrigeration systemembodied in a low temperature process for liquefaction and separation ofgaseous mixtures.

With reference to the drawing, air under elevated pressure enters thecycle through conduit and, after passing through switch valve 11, isconducted by conduit 12 for flow through passageway 13 of switching heatexchange device 14 in countercurrent heat interchange with relativelycold oxygen and nitrogen component gases as described below. Thecompressed air leaves the cold end of the heat exchange device 14-through conduit 15 and may be close to saturation temperature at theexisting pressure. The cold air passes through valved manifold 16 andthen by conduit 17 to the base of a high pressure fractionating columnor section 18 providing a zone including liquid-vapor contact means suchas fractionating plates 19 wherein the air undergoes preliminaryseparation producing liquid high boiling point fraction, crude oxygen,collecting in a pool 20, and gaseous low boiling 3,327,488 Patented June27, 1967 point fraction, essentially pure nitrogen, which flows upwardlyand is liquefied in a refluxing condenser 21. The liquefied nitrogenprovides reflux for the high pressure column and also collects in pool22 from which it is withdrawn by conduit 23 and, after pressurereduction in valve 24, is introduced as reflux into the top of a lowpressure fractionating column or section 25. The low pressure columnprovides a fractionating zone including a series of liquid-vapor contactmeans such as fractionating plates 26 wherein occurs further separationof liquid high boiling point fraction withdrawn from the pool 20 and fedthereto by conduit 27 and pressure reducing valve 28, the liquid oxygencomponent collecting in a pool 23 surrounding the refluxin-g condenser21 and gaseous high boiling point nitrogen being withdrawn from the domeof the low pressure column through conduit 30.

The conduit 30 leads to valved manifold 31 from which the cold nitrogengas flows by conduit 32 through passageway 33 of the heat exchangedevice 14 in countercurrent heat interchange with the air feed asdescribed above, the nitrogen gas leaving the warm end of the heatexchange device 14 through conduit 34 at about ambient temperature and,upon passing through the switching valve 11 is discharged from theprocess through conduit 34. Gaseous oxygen component is withdrawn fromthe low pressure column from above the pool 29 through conduit 35 andconducted thereby for flow through passageway 36 of the heat exchangedevice 14 in countercurrent heat interchange with the incomingcompressed air feed, the gaseous oxygen leaving the warmed end of theheat exchange device through conduit 37 at about ambient temperature.The switching valve 11 is operated periodically to alternate the flow ofthe air feed and the gaseous nitrogen component between the heatexchange passageways 13 and 33 and the manifolds 16 and 31 are providedwith pressure responsive valves for directing the flow of air fromconduits 15 or 32 to the conduit 17 and for directing the nitrogen flowfrom conduit 30 to conduits 15 or 32. A stream of high pressure nitrogengas is withdrawn from the refluxing condenser 21 through conduit 40 andconducted by conduit 41 for flow through unbalancing passageway 42 ofthe heat exchange device 14. The high pressure nitrogen gas is warmedupon flowing through the unbalancing passageway to an optimumtemperature for subsequent work expansion and is conducted by conduit 43to the inlet of expansion engine 44. The effluent of the expansionengine 44 is conducted by conduit 45, provided with a control valve 46,and merged with the nitrogen gas in conduit 30 for flow therewiththrough the passageway 33 of the heat exchange device 14 to providerefrigeration for the air feed.

The low temperature process described above incorporates the novelrefrigeration cycle of the present invention which makes it possible towithdraw from the process component product in liquid phase; forexample, liquid oxygen withdrawn from the pool 29 through valved conduit50. The novel refrigeration cycle includes an expansion engine 51 fedwith high pressure fluid previously warmed by heat interchange witheffluent of the expansion engine 44. As shown, the conduit 40 feeds abranch conduit 52 having a control valve 53 leading to passageway 54 ofheat exchange device 55 and the passageway 54 is connected by conduit 56to the inlet of the expansion engine 51, effluent of the latterexpansion engine being connected by conduit 57 having a control valve 58to the conduit 45. The low pressure side of the expansion engine 44 isconnected by conduit 59, provided with a control valve 60, for flowthrough passageway 61 of the heat exchange device 55 in countercurrentheat interchange with the high pressure nitrogen gas flowing through thepassageway 54, the other end of the passageway 61 being connected byconduit 62 to the conduit 38. The feature of utilizing effluent of afirst expansion engine to warm the feed of a second expansion enginemakes it possible to obtain optimum refrigeration upon work expansion ofa given mass of high pressure fluid and the first or both of theexpansion engines may be operated to provide different levels ofrefrigeration without material adjustment of process parameters.

As an example of an operating cycle, a quantity of nitrogen gascorresponding to about 10% of the air feed is withdrawn from therefluxing condenser 21 under a pressure of about 75 p.s.i.a. and atemperature of about 290 F. and flowed through the unbalancingpassageway 42 wherein the high pressure nitrogen gas is warmed to about100 F. The thus warmed nitrogen gas is expanded in the expansion engine44 to about 26 p.s.i.a. and thereby cooled to about 197 F. with valve 46closed and valve 60 open, the effluent of the expansion engine 44 flowsthrough the passageway 61 in countercurrent heat interchange with highpressure nitrogen gas in the passageway 54 of a mass equal to about ofthe air feed. The effluent leaves the passageway 61 at about 280 F. andis merged by way of conduit 62 with the low pressure nitrogen gas inconduit 30, while the high pressure nitrogen gas leaves the passageway54 at about 207 F. and at that temperature is expanded in the expansionengine 51 to about 20 p.s.i.a. and cooled to about 290" F. The efiluentfrom the latter expansion engine is passed through conduit 57 and opencontrol valve 58 to conduit 45 and merged with the low pressure nitrogengas in conduit 30. Of course, if it is not desired to withdraw liquidproduct from the cycle, additional refrigeration would not be requiredand the expansion engine 51 would not be operated. In such case,effluent from the expansion engine 44 would flow past open valve 46 andthrough conduit 45 to the conduit 30 and the valves 53 and 60 would beclosed. The path of flow of effluent of the expansion engine 44 couldinclude the passageway 61 whether the expansion engine 51 is or is notoperating. The refrigeration produced by the expansion engine 44 isgreater than the refrigeration produced by the expansion engine 51 forfluids of the same mass and pressure due to the pre-expansiontemperatures. However, the total refrigeration obtained from theexpansion engines 44 and 51 when the efiluent of one is used to warm thefeed to the other is substantially greater than if the expansion engineswere operated in series or fed in parallel with high pressure fluidwarmed to a uniform intermediate temperature. In the environment of alow temperature separation process, the present invention makes itpossible to provide a given quantity of refrigeration by makingavailable more reflux for the separation, as compared to priorrefrigeration systems employing parallel connected expansion engines. Aportion or all of the high pressure fluid fed to the expansion engines44 and 51 may be derived from the high pressure column other than therefluxing condenser. For example, high pressure gas may be withdrawnfrom the high pressure column above the feed point by a conduit 70having a control valve 71 and merged with the conduit 41 and controlvalves 72 and 73 may be provided in conduits 40 and 41, respectively.

Although the novel refrigeration system provided by the presentinvention is disclosed in combination with a low temperature separationprocess, it will be appreciated the system may be employed in otherenvironments in which cooled high pressure fluid is work expanded in twozones with the high pressure fluid expanded in a first zone beingprewarmed upon heat interchange with a process stream to be refrigeratedand with the high pressure fluid expanded in the second zone beingprewarmed upon heat interchange with eflluent from the first expansionzone. Moreover, although the invention has been described in connectionwith a low temperature process for separation of air, it has utilitywith low temperature processes for separating other gaseous mixtures.Reference therefore will be had to the appended claims for a definitionof the limits of the invention.

What is claimed is: 1. Process for producing refrigeration comprisingthe steps of passing a first stream of compressed cold gas at a firstrelatively high pressure in heat interchange with a first relativelywarm fluid to warm the first stream of compressed gas to a relativelyhigh temperature, expanding the warm first stream of compressed gas atthe relatively high temperature and under the first relatively highpressure with production of external work to produce first efliuentunder, a first relatively low pressure, passing a second stream of;compressed cold gas at substantially the first relatively high pressurein countercurrent heat exchange with first efliuent to cool the firstefiluent and to warm the second stream of compressed gas to atemperature lower than the relatively high temperature of the warm firststream of compressed gas, expanding the warm second stream of compressedgas with production of external work to produce second eflluent at atemperature lower than the temperature of the first effluent and under apressure corresponding to the first relatively low pressure ofthe firstefl'luent, the first efiiuent being cooled to a temperature approachingthe temperature of the second efiiuent by the heat interchange with thesecond stream of compressed gas, and passing the cooled first eflluentand the second effiuent to a common utilization zone. 2. Process forproducing refrigeration as defined in claim 1 in which the first streamof compressed gas and the second stream of compressed gas are derivedfrom a common source of compressed gas.

3. Process for producing refrigeration as defined in claim 1 in whichthe common utilization zone comprises a heat exchange zone wherein thecooled first diluent and the second eflluent are passed in heatinterchange with a fluid to be cooled.

4. Process for producing refrigeration as defined in claim 3 in whichthe first stream of compressed gas and the second stream of compressedgas are derived from the fluid to be cooled following heat interchangewith the cooled first eflluent and the second efliuent.

5. Process for separating gaseous mixtures in a low pressure operationincluding preliminary separation in a high pressure fractionating zoneand further separation in a low pressure fractionating zone whichcomprises the steps of passing compressed gaseous mixture through a heatexchange zone of the operation in heat interchange with a least coldfluid withdrawn from the low pres sure fractionating zone to cool thecompressed gaseous mixture,

withdrawing cool gaseous mixture from the heat exchange zone,

feeding cold gaseous mixture withdrawn from the heat exchange zone tothe high pressure fractionating zone,

deriving a first stream of cold fluid under a first pressure from coldgaseous mixture withdrawn from the heat exchange zone,

passing the first stream of cold fluid in heat interchange with thegaseous mixture in the heat exchange zone to warm the first stream,

expanding the warm first stream under the firs-t pressure withproduction of external work to provide afirst effluent,

deriving a second stream of cold fluid at substantially the firstpressure from cold gaseous mixture withdrawn from the heat exchangezone,

5 6 passing first effluent in countercurrent heat exchange ReferencesCited with the second stream of cold fluid to warm the UNITED STATESPATENTS second stream of fluid and cool the first efiiuent, expandingthe warm second stream of fluid with pro- 2838918 6/1958 Becker et 52-49X duction of external work to provide a second effiuent 5 FOREIGNPATENTS at a pressure corresponding to the pressure of the 498,441 12/1953 Canada, first efliuent and at a temperature lower than the1,019,664 11/1957 Germany. temperature of the first efliuent, 912,47212/ 1962 Great Britain.

and passing cool first efliuent and second efiluent to a NORMAN YUDKOFFPrimary Examiner Common Zone of the Opera/Hon V. W. PRETKA, AssistantExaminer.

1. PROCESS FOR PRODUCING REFRIGERATION COMPRISING THE STEPS OF PASSING AFIRST STREAM OF COMPRESSED COLD GAS AT A FIRST RELATIVELY HIGH PRESSUREIN HEAT INTERCHANGE WITH A FIRST RELATIVELY WARM FLUID TO WARM THE FIRSTSTREAM OF COMPRESSED GAS TO A RELATIVELY HIGH TEMPERATURE, EXPANDING THEWARM FIRST STREAM OF COMPRESSED GAS AT THE RELATIVELY HIGH TEMPERATUREAND UNDER THE FIRST RELATIVELY HIGH PRESSURE WITH PRODUCTION OF EXTERNALWORK TO PRODUCE FIRST EFFLUENT UNDER A FIRST RELATIVELY LOW PRESSURE,PASSING A SECOND STREAM OF COMPRESSED COLD GAS AT SUBSTANTIALLY THEFIRST RELATIVELY HIGH PRESSURE IN COUNTERCURRENT HEAT EXCHANGE WITHFIRST EFFLUENT TO COOL THE FIRST EFFLUENT AND TO WARM THE SECOND STREAMOF COMPRESSED GAS TO TEMPERATURE LOWER THAN THE RELATIVELY HIGHTEMPERATURE OF THE WARM FIRST STREAM OF COMPRESSED GAS, EXPANDING THEWARM SECOND STREAM OF COMPRESSED GAS WITH PRODUCTION OF EXTERNAL WORK TOPRODUCE SECOND EFFLUENT AT A TEMPERATURE LOWER THAN THE TEMPERATURE OFTHE FIRST EFFLUENT AND UNDER A PRESSURE CORRESPONDING TO THE FIRSTRELATIVELY LOW PRESSURE OF THE FIRST EFFLUENT, THE FIRST EFFLUENT BEINGCOOLED TO A TEMPERATURE APPROACHING THE TEMPERATURE OF THE SECONDEFFLUENT BY THE HEAT INTERCHANGE WITH THE SECOND STREAM OF COMPRESSEDGAS, AND PASSING THE COOLED FIRST EFFLUENT AND THE SECOND EFFLUENT TO ACOMMON UTILIZATION ZONE.